Method for producing silicon epitaxial wafer and silicon epitaxial wafer

ABSTRACT

It is to provide a method for producing a silicon epitaxial wafer, which can prevent fine unevenness from occurring on a rear main surface of a silicon epitaxial wafer and which suppresses the haze level of the whole rear main surface to 50 ppm or less. 
     A method for producing a silicon epitaxial wafer, includes: a hydrogen heat treatment step of arranging within a reactor a susceptor capable of mounting a silicon single crystal substrate and subjecting the silicon single crystal substrate mounted on the susceptor to heat treatment in a hydrogen atmosphere, and a vapor phase epitaxy step of epitaxially growing a silicon epitaxial layer after the hydrogen heat treatment step, wherein the silicon single crystal substrate is separated from the susceptor during the hydrogen heat treatment step, and the silicon single crystal substrate is mounted on the susceptor during the vapor phase epitaxy step.

TECHNICAL FIELD

The present invention relates to a method for producing a siliconepitaxial wafer. The present invention also relates to a siliconepitaxial wafer.

BACKGROUND ART

Conventionally, there is known a method for producing a siliconepitaxial wafer by epitaxially growing a silicon epitaxial layer on afront main surface of a silicon single crystal substrate mounted on aspot facing of a susceptor arranged within a reactor.

In a case of producing the silicon epitaxial wafer, a cleaning step ofcleaning the silicon single crystal substrate is performed before vaporphase epitaxy of the silicon epitaxial layer. In the cleaning step,generally, an SC1 cleaning step of mainly removing particles isperformed using a mixed solution composed of ammonia water and hydrogenperoxide solution and then, an SC2 cleaning step of mainly removingmetals is performed using a mixed solution composed of hydrochloric acidand hydrogen peroxide solution. During the SC1 cleaning and the SC2cleaning, a natural oxide film is formed on a surface of the siliconsingle crystal substrate.

Thereafter, the cleaned silicon single crystal substrate is carriedwithin the reactor and mounted on the spot facing of the susceptor.Further, heating within the reactor is performed to subject thesubstrate to hydrogen heat treatment. As a result, the natural oxidefilm formed on the front main surface of the silicon single crystalsubstrate is removed by etching using a hydrogen gas. In the hydrogenheat treatment, a hydrochloric gas may be used together with a hydrogengas.

Next, a temperature within the reactor is set to a growth temperatureand a silicon source gas is fed on the front main surface of the siliconsingle crystal substrate. As a result, the silicon epitaxial layer isepitaxially grown on the front main surface of the silicon singlecrystal substrate. Thus, the silicon epitaxial wafer is produced.

Further, there is known a wafer supporting apparatus for forming a thinfilm on a rear surface of a wafer, in which projections for supportingthe wafer from its lower surface are provided on tops of lift pins forforming a clearance between the wafer and a susceptor (see, e.g., PatentDocument 1).

Patent Document 1: Japanese Patent Application Publication UnexaminedTokukaihei-9-205130

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

Incidentally, fine unevenness may be formed on a rear main surface of asilicon epitaxial wafer. Particularly, in a silicon epitaxial waferproduced by epitaxially growing a silicon epitaxial layer on a frontmain surface of a double-sided mirror silicon single crystal substrateof which both the main surfaces are subjected to a mirror polishingfinish, the fine unevenness is observed as haze under a collimated lightor by an optical surface inspection apparatus.

The present invention is made in order to solve the above-describedproblems. An object of the present invention is to provide a method forproducing a silicon epitaxial wafer, which can prevent fine unevennessfrom occurring on a rear main surface of a silicon epitaxial wafer,particularly, a silicon epitaxial wafer produced by epitaxially growinga silicon epitaxial layer on a front main surface of a double-sidedmirror silicon single crystal substrate and which can improve a hazelevel on the rear main surface of the silicon epitaxial wafer. Anotherobject of the present invention is to provide a silicon epitaxial waferwhich can be produced by the producing method.

Means for Solving the Problem

As described above, fine unevenness is formed, particularly, on the rearmain surface of the silicon epitaxial wafer produced by epitaxiallygrowing the silicon epitaxial layer on the front main surface of thedouble-sided mirror silicon single crystal substrate. It can beunderstood that the reason for the above is as follows.

In the production of the silicon epitaxial wafer, hydrogen heattreatment is performed before the vapor phase epitaxy of the siliconepitaxial layer as described above. During the hydrogen heat treatment,the front main surface of the silicon single crystal substrate is etchedby a hydrogen gas as well as the hydrogen gas goes around to a clearancebetween an upper surface of a spot facing of a susceptor and a rear mainsurface of the silicon single crystal substrate housed in the spotfacing, and as a result, a natural oxide film on the rear main surfaceof the silicon single crystal substrate is locally etched. Particularlyin portions of the rear main surface facing lift pin through-holesformed on the susceptor, the natural oxide film is easily etched.

When epitaxially growing the silicon epitaxial layer in a state wherethe natural oxide film is thus etched locally to generate etchingunevenness, the silicon epitaxial layer is epitaxially grown in spots ona place where silicon which constitutes the rear main surface of thesilicon single crystal substrate is locally exposed, and as a result,fine unevenness is formed on the rear main surface.

Thus, a method for producing a silicon epitaxial wafer according to afirst aspect of the present invention comprises a hydrogen heattreatment step of arranging a susceptor capable of mounting a siliconsingle crystal substrate within a reactor and subjecting the siliconsingle crystal substrate mounted on the susceptor to heat treatment in ahydrogen atmosphere; and a vapor phase epitaxy step of epitaxiallygrowing a silicon epitaxial layer after the hydrogen heat treatmentstep, wherein the silicon single crystal substrate is separated from thesusceptor during the hydrogen heat treatment step, and the siliconsingle crystal substrate is mounted on the susceptor during the vaporphase epitaxy step.

When the silicon single crystal substrate is separated from thesusceptor by allowing a lift pin which vertically moves the siliconsingle crystal substrate relatively to the susceptor to support thesilicon single crystal substrate, no exclusive separation device isrequired and therefore, this way is simple.

The hydrogen heat treatment step is preferably performed at atemperature lower than a vapor phase epitaxy temperature of the siliconepitaxial layer.

Further, in the hydrogen heat treatment step, a temperature within thereactor when the silicon single crystal substrate is separated from thesusceptor is preferably at least 900° C. or more, more preferably 1000°C. or more. On the other hand, the temperature within the reactor ispreferably less than 1150° C., more preferably 1100° C. or less.

Further, when the method comprises a cleaning step of cleaning thesilicon single crystal substrate before the hydrogen heat treatmentstep, it is preferable that the cleaning step has rear main surfacenatural oxide film removal cleaning for removing a natural oxide filmformed at least on the rear main surface of the silicon single crystalsubstrate, and the rear main surface natural oxide film removal cleaningis performed as final cleaning in the cleaning step.

Further, in this case, the cleaning step may have both main surfacesnatural oxide film removal cleaning for removing a natural oxide filmformed on both the main surfaces of the silicon single crystal substrateand the both main surfaces natural oxide film removal cleaning may beperformed as final cleaning.

In these cases, it is preferable that in the natural oxide film removalcleaning, the natural oxide film is cleaned and removed usinghydrofluoric acid.

On the other hand, it is preferable that the cleaning step has frontmain surface oxide film formation cleaning for forming an oxide film onthe front main surface of the silicon single crystal substrate, and thefront main surface oxide film formation cleaning is performed as finalcleaning of the front main surface.

Further, it is preferable that a time for the silicon single crystalsubstrate to be stored in air during the period that the substrate isfed into the reactor after the final cleaning is set within 3 days.

A method for producing a silicon epitaxial wafer according to a secondaspect of the present invention comprises: a cleaning step of cleaning asilicon single crystal substrate; and a vapor phase epitaxy step ofmounting the silicon single crystal substrate on a susceptor arrangedwithin a reactor with a non-oxidizing atmosphere and epitaxially growinga silicon epitaxial layer after the cleaning step, wherein in thecleaning step, front main surface oxide film formation cleaning forforming an oxide film on a front main surface of the silicon singlecrystal substrate is performed as final cleaning of the front mainsurface and rear main surface natural oxide film removal cleaning forremoving a natural oxide film formed on a rear main surface of thesilicon single crystal substrate is performed as final cleaning of therear main surface.

When the rear main surface natural oxide film removal cleaning isperformed as the final cleaning in the cleaning step, the time for thesilicon single crystal substrate to be stored in air during the periodthat the substrate is fed into the reactor after the final cleaning ispreferably set within 6 hours in order to prevent a natural oxide filmformed during the period up to the subsequent vapor phase epitaxy frombecoming thick.

Further, the silicon single crystal wafer is preferably a double-sidedmirror silicon single crystal substrate of which both the main surfacesare subjected to a mirror polishing finish.

According to the method for producing a silicon epitaxial wafer inaccordance with the first or second aspect of the present invention, anatural oxide film on the rear main surface of the silicon singlecrystal substrate, particularly, of the double-sided mirror siliconsingle crystal substrate can be evenly etched. Therefore, in thesubsequent vapor phase epitaxy step, fine unevenness can be preventedfrom occurring on the rear main surface of the substrate, particularly,on the portions of the rear main surface facing the lift pinthrough-holes formed on the spot facing, so that no haze can be observedunder a collimated light or by an optical surface inspection apparatus.As a result, there can be produced a silicon epitaxial wafer comprising:

a silicon single crystal substrate, particularly, a double-sided mirrorsilicon single crystal substrate of which both the main surfaces aresubjected to a mirror polishing finish, and

a silicon epitaxial layer formed on a front main surface of thesubstrate, wherein a haze level of the whole rear main surface is 0.1ppm to 50 ppm, more preferably 0.1 ppm to 0.5 ppm.

When the haze level on the whole rear main surface is 50 ppm or less, nohaze is detected by a visual inspection under a collimated light in adark room. Further, when the haze level on the whole rear main surfaceis 0.5 ppm or less, particles having a diameter of 0.18 μm or more onthe rear main surface can be measured using an optical surfaceinspection apparatus.

In the above description, ppm is a unit expressing an intensity ofscattered light obtained by optically scanning the rear main surface ofthe silicon epitaxial wafer using an optical surface inspectionapparatus such as a laser scattered light detection apparatus. In otherwords, for example, 0.1 ppm means that scattered light having anintensity of 0.1 millionth of an intensity of incident light ismeasured. Further, the intensity of scattered light is proportional to asize of surface roughness and therefore, for example, it is understoodthat when the intensity of the scattered light is large, unevenness isrelatively large.

Incidentally, the laser scattered light detection apparatus can performa measurement on the whole rear main surface of the silicon epitaxialwafer. However, at a peripheral edge of the silicon epitaxial wafer, ameasurable level of diffuse reflection light from a chamfer of the waferis simultaneously measured. Therefore, measured values obtained in arange of several millimeters in width at the peripheral edge of thesilicon epitaxial wafer are normally excluded.

The silicon epitaxial wafer is particularly preferably a high flatnesssilicon epitaxial wafer having a diameter of 300 mm or more, whichenjoys an increasing demand recently.

Herein, the wafer supporting apparatus in the above-described PatentDocument 1 has a construction of always forming a clearance between thewafer and the susceptor in order to form a thin film on the rear surfaceof the wafer. In the present invention, in order to evenly etch thenatural oxide film on the rear main surface of the silicon singlecrystal substrate, particularly, of the double-sided mirror siliconsingle crystal substrate, the substrate is separated from the susceptorin subjecting the substrate to hydrogen heat treatment. On the otherhand, the substrate is mounted on the susceptor in epitaxially growingthe silicon epitaxial layer on the front main surface of thedouble-sided mirror silicon single crystal substrate. In other words,there is used a construction such that the substrate and the susceptorare not separated from each other during the vapor phase epitaxy. Inshort, the object and construction of the present invention aredifferent from those of the invention disclosed in the PatentDocument 1. According to the present invention, the natural oxide filmon the rear main surface of the substrate can be evenly etched beforethe vapor phase epitaxy as well as the silicon epitaxial layer can beprevented from being epitaxially grown in spots on the rear main surfaceof the substrate.

EFFECT OF THE INVENTION

According to the present invention, a natural oxide film on a rear mainsurface of a silicon single crystal substrate can be evenly etched.Therefore, in the subsequent vapor phase epitaxy step, fine unevennesscan be prevented from occurring on the rear main surface of thesubstrate, particularly, on the portions of the rear main surface facingthe lift pin through-holes, and as a result, a haze level of the wholerear main surface of the silicon epitaxial wafer can be suppressed to 50ppm or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for illustrating each step of a method for producing asilicon epitaxial wafer exemplified as a first embodiment to which thepresent invention is applied.

FIG. 2 is a view showing a correspondence among a temperature within areactor, each producing step and arrangement state of a substrateaccording to a method for producing a silicon epitaxial wafer in FIG. 1.

FIG. 3 is a schematic front cross-sectional view showing a vapor phaseepitaxy apparatus, and shows a state where a silicon single crystalsubstrate is mounted within a spot facing of a susceptor.

FIG. 4 is a schematic front cross-sectional view showing a vapor phaseepitaxy apparatus, and shows a state where a silicon single crystalsubstrate is separated from a susceptor by a lift pin.

FIG. 5 is a view for illustrating each step of a method for producing asilicon epitaxial wafer exemplified as a second embodiment to which thepresent invention is applied.

FIG. 6A is a view schematically showing a haze level on a rear mainsurface of a silicon epitaxial wafer in Example 1.

FIG. 6B is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer in Comparative Example 1.

FIG. 7A is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Experiment Example.

FIG. 7B is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Experiment Example.

FIG. 7C is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Experiment Example.

FIG. 8A is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 2-1.

FIG. 8B is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 2-2.

FIG. 8C is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 2-3.

FIG. 9A is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 2-4.

FIG. 9B is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Comparative Example 2-1.

FIG. 9C is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Comparative Example 2-2.

FIG. 10A is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 3-1.

FIG. 10B is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 3-2.

FIG. 10C is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Comparative Example 3.

FIG. 11A is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 5-1.

FIG. 11B is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 5-2.

FIG. 11C is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 5-3.

FIG. 11D is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Example 5-4.

FIG. 12A is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Comparative Example 5-1.

FIG. 12B is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Comparative Example 5-2.

FIG. 12C is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Comparative Example 5-3.

FIG. 12D is a view schematically showing a haze level of a rear mainsurface of a silicon epitaxial wafer of Comparative Example 5-4.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments according to the present invention will be described belowwith reference to the accompanying drawings.

First Embodiment

First, a schematic construction of a single wafer vapor phase epitaxyapparatus 100 as one preferable example of a vapor phase epitaxyapparatus used in a method for producing a silicon epitaxial waferaccording to a first embodiment to which the present invention isapplied will be described with reference to FIG. 3.

As shown in FIG. 3, the vapor phase epitaxy apparatus 100 schematicallyincludes: a disc-like susceptor 1 which supports a double-sided mirrorsilicon single crystal substrate W during vapor phase epitaxy; a reactor2 inside which the susceptor 1 is arranged in an almost horizontal statein the inside; a susceptor supporting member 3 which supports thesusceptor 1 from its under surface side; a lift pin 4 which verticallymoves the double-sided mirror silicon single crystal substrate Wrelatively to the susceptor 1; a heating device 5 such as a halogen lampwhich heats the inside of the reactor 2; a gas introduction duct 6 whichintroduces a silicon source gas into a region above the susceptor 1within the reactor 2 to supply the gas on a front main surface of thedouble-sided mirror silicon single crystal substrate W on the susceptor1; a purge gas introduction duct 7 which is disposed on the same side asthat of the gas introduction duct 6 of the reactor 2 to introduce apurge gas into a region under the susceptor 1 within the reactor 2; andan exhaust duct 8 which is disposed on the opposite side of the reactor2 relative to the reaction gas introduction duct 6 and the purge gasintroduction duct 7 to discharge gas from the reactor 2.

On the front main surface of the susceptor 1, there is formed a spotfacing 10 inside which the double-sided mirror silicon single crystalsubstrate W where a silicon epitaxial layer is epitaxially grown ismounted.

The spot facing 10 has, for example, a two-step structure including anupper spot facing section 11 which supports the peripheral portion ofthe double-sided mirror silicon single crystal substrate W, and a lowerspot facing section 12 which is formed in a more central and lowerposition than that of the upper spot facing section 11.

Further, the susceptor 1 is made up of, for example, graphite coatedwith silicon carbide.

The susceptor supporting member 3 is provided movably in the verticaldirection A, and on the top end portion of the susceptor supportingmember 3, a plurality of support arms 3 a are provided to be branchedradially. The top end portions of the support arms 3 a are fitted intorecessed portions 1 a formed on the rear main surface of the susceptor1, thereby supporting the susceptor 1 such that the top surface thereofis almost horizontal.

Each of the lift pins 4 includes a body portion 4 a formed in a rodshape, and a head portion 4 b which is formed at the top end portion ofthe body portion 4 a to support the double-sided mirror silicon singlecrystal substrate W mounted on the spot facing 10 from the under surfaceside of the substrate W. The head portion 4 b is made larger in diameterthan the body portion 4 a so as to easily support the substrate W.

The lift pins 4 are inserted into lift pin through holes 10 a formed onthe bottom surface of the spot facing 10, and are placed such that thehead portions 4 b thereof face the bottom surface of the spot facing 10.Further, the body portions 4 a of the lift pins 4 run through thethrough-holes 3 b formed in the support arms 3 a.

Next, a method for producing a silicon epitaxial wafer according to thepresent invention will be described with reference to FIGS. 1 and 2.

In the method for producing a silicon epitaxial wafer according to thepresent embodiment, the silicon single crystal substrate W is separatedfrom the susceptor 1 using the lift pins 4 in a hydrogen heat treatmentstep (step S11; see FIG. 2) to be performed before a vapor phase epitaxystep (step S13; see FIG. 2) of epitaxially growing a silicon epitaxiallayer on a front main surface of the silicon single crystal substrate W.As a result, a natural oxide film on the rear main surface of thesilicon single crystal substrate W is evenly removed by etching.Thereafter, the silicon single crystal substrate W is mounted on thespot facing 10 and the silicon epitaxial layer is epitaxially grown onthe front main surface of the substrate W.

Example 1 and Comparative Example 1 of the present invention will bedescribed below.

Incidentally, in Example 1 and Comparative Example 1, and theafter-mentioned respective Examples and Comparative Examples, asubstrate of a p type with a diameter of 300 mm, a resistance of about0.0015 Ω·cm and plane orientation of (100) is used as the double-sidedmirror silicon single crystal substrate W. Further, a silicon epitaxiallayer having a resistance of about 10 Ω·cm is epitaxially grown to alength of about 3 μm on the front main surface of the double-sidedmirror silicon single crystal substrate W under vapor phase epitaxyconditions where a source gas is trichlorosilane and a growthtemperature is 1150° C.

Further, a haze level x on a rear main surface of the silicon epitaxialwafer is measured using an optical surface inspection apparatus (notshown), and an intensity of scattered light obtained by opticallyscanning the rear main surface is expressed by a unit of ppm.Specifically, for example, 0.1 ppm means that scattered light having anintensity of 0.1 millionth of an intensity of incident light ismeasured. Further, the intensity of the scattered light is proportionalto a size of surface roughness and therefore, for example, it isunderstood that when the intensity of the scattered light is large,unevenness is relatively large.

EXAMPLE 1

<Relation Between Separation from Susceptor and Haze Level>

(Cleaning Conditions)

The double-sided mirror silicon single crystal substrate W is subjectedto SC1 cleaning and SC2 cleaning. Incidentally, each cleaning (includinghydrofluoric acid cleaning (described later)) such as SC1 cleaning orSC2 cleaning in the cleaning step will be described in detail later.

(Hydrogen Heat Treatment Conditions Before Vapor Phase Epitaxy Step)

Example 1: In a state of separating the substrate W from the susceptor 1using the lift pins 4, the hydrogen heat treatment is performed whilekeeping the state for 120 seconds at 1130° C. (see, FIG. 6A).

Comparative Example 1: In a state of mounting the substrate W on thesusceptor 1, the hydrogen heat treatment is performed while keeping thestate for 120 seconds at 1130° C. (see FIG. 6B).

The measurement results of the haze level x on the rear main surface ofthe silicon epitaxial wafer produced under the above-describedconditions are shown in FIGS. 6A and 6B.

[Evaluation]

As shown in FIG. 6B, the rear main surface of the silicon epitaxialwafer in Comparative Example 1 has regions where a haze level x islarger than 0.2 ppm and reaches several hundred ppm. Particularly, hazelevels x at portions of the rear main surface facing the lift pinthrough-holes deteriorate. However, as shown in FIG. 6A, it isunderstood that when separating the double-sided mirror silicon singlecrystal substrate W from the susceptor 1 during the hydrogen heattreatment step (Example 1), the haze level x on the rear main surface ofthe silicon epitaxial wafer is from 0.1 ppm to 0.2 ppm and is improvedas compared with that of Comparative Example 1.

Experiment Example

Incidentally, when supporting the double-sided mirror silicon singlecrystal substrate W by the lift pins 4 to separate the substrate W fromthe susceptor 1 and subjecting the substrate W to hydrogen heattreatment at a high temperature of 1150° C. or more, a stress isconcentrated on places of the substrate W supported by the lift pins 4and as a result, crystal defects such as slip dislocation may be inducedin the substrate W.

Accordingly, in the present embodiment, a treatment temperature islowered than a vapor phase epitaxy temperature to subject the substrateW to the hydrogen heat treatment and as a result, the induction of theslip dislocation is suppressed. However, when the hydrogen heattreatment temperature is excessively lowered, removal of a natural oxidefilm formed on the rear main surface of the substrate W is hardlyperformed sufficiently in the hydrogen heat treatment step. As a result,the haze level x on the rear main surface of the silicon epitaxial waferdeteriorates as shown in FIGS. 7A to 7C.

Herein, FIGS. 7A to 7C show measurement results, using an opticalsurface inspection apparatus, of the haze level x on the rear mainsurface of the silicon epitaxial wafer produced by subjecting thesubstrate W to hydrogen heat treatment while changing the treatmenttemperature (temperature within the reactor) on the double-sided mirrorsilicon single crystal substrate W to 1150° C. (FIG. 7A), 1100° C. (FIG.7B) and 1050° C. (FIG. 7C) and then by epitaxially growing a siliconepitaxial layer on the front main surface of the substrate W.

As shown in FIG. 7C, when subjecting the substrate W to the hydrogenheat treatment while setting the treatment temperature to 1050° C.,removal of a natural oxide film formed on the rear main surface of thesubstrate W cannot be sufficiently performed, and as a result, the hazelevel x on the rear main surface of the silicon epitaxial wafer isscarcely improved.

On this occasion, before the hydrogen heat treatment step, natural oxidefilm removal cleaning (step S5) may be performed as final cleaning inthe cleaning step (steps S1 to S7; see FIG. 1) of cleaning the substrateW to previously remove the natural oxide film formed on the surface ofthe substrate W.

Herein, the double-sided mirror silicon single crystal substrate W is,for example, a substrate prepared in accordance with the followingsteps.

That is, a silicon single crystal ingot manufactured, for example, by aFZ (floating zone) method or a CZ (Czochralski) method is sliced using aslicer. After subjecting an edge of the sliced wafer to chamfering, boththe surfaces are lapped and further subjected to chemical etchingtreatment. Further, both the main surfaces of the wafer after completionof the etching step are subjected to a mirror polishing finish bymechanochemical polishing. Thus, the double-sided mirror silicon singlecrystal substrate W is produced.

Further, in the cleaning step of the double-sided mirror silicon singlecrystal substrate W prepared as described above, the SC1 cleaning isfirst performed as shown in FIG. 1 (step S1). In the SC1 cleaning, thedouble-sided mirror silicon single crystal substrate W is dipped into anSC1 chemical liquid tank filled with SC1 cleaning chemicals comprising amixed solution composed of hydrogen peroxide solution (H₂O₂), ammoniawater (NH₄OH) and purified water to thereby mainly remove particlesadhered to the substrate W.

Next, the substrate W is dipped into a purified water tank to be rinsedwith purified water (step S2). The pure water rinse is repeated, forexample, twice.

Subsequently, SC2 cleaning is performed (step S3). In the SC2 cleaning,the double-sided mirror silicon single crystal substrate W is dippedinto an SC2 chemical liquid tank filled with SC2 cleaning chemicalscomprising a mixed solution composed of a hydrogen peroxide solution(H₂O₂), hydrochloric acid (HCl) and purified water to thereby mainlyremove metal contaminations adhered to the substrate W.

Next, the substrate W is dipped into a purified water tank to be rinsedwith purified water (step S4). The pure water rinse is repeated, forexample, twice.

Next, hydrofluoric acid cleaning is performed (step S5) as natural oxidefilm removal cleaning for removing a natural oxide film formed on boththe main surfaces of the substrate W. Specifically, the substrate W withnatural oxide films formed on both the main surfaces thereof by the SC1cleaning and the SC2 cleaning is dipped into a hydrofluoric acidchemical liquid tank in a predetermined concentration to thereby evenlyremove by etching the natural oxide films on both the main surfaces ofthe substrate W.

Further, the substrate W is dipped into a purified water tank to berinsed with purified water (step S6). The pure water rinse is repeated,for example, twice.

Subsequently, the substrate W is dried (step S7). Thus, the cleaning ofthe substrate is completed.

Afterwards, the hydrogen heat treatment step and the vapor phase epitaxystep are performed, for example, using the vapor phase epitaxy apparatus100 (FIG. 2).

Specifically, first, a hydrogen (H₂) gas is introduced into the reactor2 as well as a temperature within the reactor 2 is set to a feedingtemperature (e.g., about 650° C.) of the substrate W.

Next, the substrate W is fed into the reactor 2 (step S8). Specifically,first, the respective lift pins 4 are raised relatively to the susceptor1 so as to protrude upward above the upper surface of the susceptor 1 byalmost the same amount as each other. In other words, the susceptor 1 islowered along with an operation of lowering the susceptor supportingmember 3, the lower edges of the lift pins 4 reach, for example, thebottom surface of the reactor 2 in the course of this lowering, andwhile the lift pins 4 cannot be lowered any further, the susceptor 1 isfurther lowered. Thus, the lift pins 4 are raised relatively to thesusceptor 1, which results in a state in which the substrate W is absentin FIG. 4.

Further, the substrate W is conveyed into the reactor 2 by a handler(not shown) and, with the front main surface up, the substrate W issupported by the head portions 4 b of the respective lift pins 4. Then,the handler is put back. Thus, the substrate W is fed into the reactor2. As a result, as shown in FIG. 4, the substrate W is brought into astate of being separated from the susceptor 1 by the lift pins 4 (stepS9). At this time, the susceptor 1 and the substrate W are brought intoa state of being separated, for example, with a clearance of at least 1mm from one another.

Next, the reactor 2 inside is heated (elevated in temperature) to thehydrogen heat treatment temperature which is considered to be atemperature lower than the after-mentioned vapor phase epitaxytemperature of the silicon epitaxial layer (step S10) to perform thehydrogen heat treatment (step S11). Specifically, in the hydrogen heattreatment, a state of separating the substrate W from the susceptor 1 iskept at a predetermined temperature for a predetermined time within thereactor 2 with a hydrogen atmosphere, and as a result, a natural oxidefilm formed on the rear main surface of the substrate W after thecleaning step is removed by etching using hydrogen. Accordingly, thenatural oxide film on the rear main surface of the substrate W can beevenly removed surely.

Herein, a temperature within the reactor 2 when separating the substrateW from the susceptor 1 is preferably from 900 to less than 1150° C. (seeFIGS. 8A to 8C and FIGS. 9A to 9C: for details, described later). In thehydrogen heat treatment at less than 900° C., the natural oxide filmcannot be removed sufficiently and therefore, the haze level on the rearmain surface of the silicon epitaxial wafer is scarcely improved. On theother hand, in the hydrogen heat treatment at 1150° C. or more, crystaldefects such as slip dislocation occur frequently. In the hydrogen heattreatment step, a treatment at 1100° C. or less is more preferable forsuppressing occurrence of crystal defects such as slip dislocation, anda temperature at 1000° C. or more is more preferable for keeping a hazelevel on the rear main surface to 50 ppm or less.

Further, a time for keeping a state of separating the substrate W fromthe susceptor 1 is preferably from 10 to 120 seconds. When the time isshorter than 10 seconds, the natural oxide film cannot be sufficientlyremoved by etching. Also when the time is longer than 120 seconds,little effect is exerted on further improvement of a haze level.

Further, after a predetermined time passes in a state of separating thesubstrate W from the susceptor 1, the susceptor 1 is raised along withan operation of raising the susceptor supporting member 3. Further, whenan upper surface of the upper spot facing section 11 of the spot facing10 reaches the rear main surface of the substrate W in the course of theraising-up of the susceptor 1, the substrate W which has so far beensupported on the head portions 4 b of the lift pins 4 moves into a stateof being supported by the upper surface of the upper spot facing section11. As a result, the substrate W comes into a state of being mounted onthe spot facing 10 (step S12).

Further, when upper edges of lift pin 4 through-holes 10 a reach thehead portions 4 b of the lift pins 4, the lift pins 4 which have so farbeen supported, for example, by the bottom surface of the reactor 2 moveinto a state of being supported by the susceptor 1.

Further, the substrate W is further subjected to the hydrogen heattreatment for a predetermined time in a state of being mounted on thespot facing 10 of the susceptor 1, and as a result, the natural oxidefilm on the front main surface of the substrate W is completely removed.Thus, the hydrogen heat treatment is completed.

Next, the silicon epitaxial layer is epitaxially grown on the front mainsurface of the substrate W (step S13). Specifically, a temperaturewithin the reactor 2 is set to a growth temperature (e.g., about 1150°C.) and a silicon source gas (e.g., trichlorosilane) introduced into thereactor 2 through the gas introducing duct 6 is supplied on the frontmain surface of the substrate W. Thus, the silicon epitaxial layer isepitaxially grown on the front main surface of the substrate W toproduce the silicon epitaxial wafer.

Next, a temperature within the reactor 2 is cooled (dropped intemperature) up to a take-out temperature (e.g., about 650° C. which isthe same as the substrate feeding temperature described above) (stepS14), and then, the silicon epitaxial wafer is taken out from thereactor 2 inside (step S15).

As described above, according to the first embodiment, the substrate Wis subjected to natural oxide film removal cleaning as final cleaning inthe cleaning step before the vapor phase epitaxy, so that the naturaloxide film formed on both the main surfaces of the substrate W can beremoved. As a result, the natural oxide film formed on the surface ofthe substrate W during the storing in the air or during the cleaning canbe once removed completely. Therefore, the substrate W has on both themain surfaces thereof only a relatively thin natural oxide film formedduring the period that the substrate W is fed into the reactor 2 afterthe natural oxide film removal cleaning. Accordingly, even whenperforming the hydrogen heat treatment at the treatment temperaturelower than the vapor phase epitaxy temperature of the silicon epitaxiallayer during the hydrogen heat treatment step, the natural oxide film onthe rear main surface of the substrate W can be surely removed. Further,the temperature within the reactor 2 when separating the substrate Wfrom the susceptor 1 by the lift pins 4 is set to less than 1150° C., sothat occurrence of the crystal defects such as slip dislocation can besuppressed.

Accordingly, the natural oxide film formed on the rear main surface ofthe substrate W can be evenly removed by etching. Therefore, in thesubsequent vapor phase epitaxy step, fine unevenness can be preventedfrom occurring on the rear main surface of the substrate W,particularly, on the portions of the rear main surface facing the liftpin 4 through-holes 10 a. As a result, no haze is observed under acollimated light or by an optical surface inspection apparatus. However,when the substrate W is stored in the air for 3 days or more after thenatural oxide film removal cleaning, there is a high possibility that athick natural oxide film is formed. Therefore, it is preferred toperform again the natural oxide film removal cleaning before feeding thesubstrate W into the reactor 2 (see, FIGS. 10A to 10C).

Example 2 and Comparative Example 2 of the present invention will bedescribed below.

EXAMPLE 2

[Relation Between Hydrogen Heat Treatment Temperature and Haze Level]

(Storage Time After Hydrofluoric Acid Cleaning)

A double-sided mirror silicon single crystal substrate W which is storedfor 34 hours in the air after the hydrofluoric acid cleaning is used.

(Hydrogen Heat Treatment Conditions)

Example 2: The substrate W is subjected to the hydrogen heat treatmentwhile changing the treatment temperature to 900° C. (FIG. 8A: Example2-1), 1000° C. (FIG. 8B: Example 2-2), 1050° C. (FIG. 8C: Example 2-3)and 1100° C. (FIG. 9A: Example 2-4). At this time, in a state ofseparating the substrate W from the susceptor 1, each hydrogen heattreatment is performed while keeping the state for 60 seconds at eachtreatment temperature.

Comparative Example 2: The treatment temperature is set to 1150° C., andin a state of separating the substrate W from the susceptor 1, thehydrogen heat treatment is performed while keeping the state for 60seconds (FIG. 9B: Comparative Example 2-1), or in a state of mountingthe substrate W on the susceptor 1, the hydrogen heat treatment isperformed while keeping the state for 60 seconds (FIG. 9C: ComparativeExample 2-2).

Measurement results of the haze level x on the rear main surface of thesilicon epitaxial wafer produced under the above-described conditionsare shown in FIGS. 8A to 8C and FIGS. 9A to 9C.

[Evaluation]

As shown in FIGS. 8A to 8C and FIGS. 9A and 9B, when subjecting thesubstrate W to the hydrogen heat treatment by separating the substrate Wfrom the susceptor 1 and by setting a treatment temperature within thereactor 2 to from 900° C. to 1150° C., the haze level x on the rear mainsurface of the silicon epitaxial wafer can be improved, as compared withan example of subjecting the substrate W to the hydrogen heat treatmentin a state of mounting the substrate W on the susceptor 1 (see, FIG. 9C:Comparative Example 2-2).

However, when the hydrogen heat treatment temperature is 1150° C. (see,FIG. 9B: Comparative Example 2-1) or more, crystal defects such as slipdislocation occur frequently. Therefore, when the hydrogen heattreatment temperature is set to less than 1150° C. or more preferably to1100° C. or less as shown in FIG. 9A (Example 2-4), occurrence of thecrystal defects such as slip dislocation can be suppressed. Further, asshown in FIG. 8A (Example 2-1), when the hydrogen heat treatmenttemperature is set to 900° C. or more, the haze level on the whole rearmain surface of the silicon epitaxial wafer can be kept to from 0.1 to50 ppm. Further, as shown in FIG. 8C (Example 2-3), when the hydrogenheat treatment temperature is set to 1050° C. or more, the haze level onthe whole rear main surface of the silicon epitaxial wafer can be keptto from 0.1 to 0.5 ppm.

Example 3 and Comparative Example 3 of the present invention will bedescribed below.

EXAMPLE 3

[Relation Between Storage Time After Hydrofluoric Acid Cleaning and HazeLevel]

(Storage Time After Hydrofluoric Acid Cleaning)

The hydrofluoric acid cleaning as the natural oxide film removalcleaning is performed as final cleaning in the cleaning step, and thedouble-sided mirror silicon single crystal substrate W after thehydrofluoric acid cleaning is stored in the air for 34 hours (FIG. 10A:Example 3-1), 64 hours (FIG. 10B: Example 3-2) and 120 hours (FIG. 10C:Comparative Example 3).

(Hydrogen Heat Treatment Conditions)

The hydrogen heat treatment temperature is set to 1050° C., and in astate of separating the substrate W from the susceptor 1, each hydrogenheat treatment is performed while keeping the state for 60 seconds

Measurement results of the haze level x on the rear main surface of thesilicon epitaxial wafer produced under the above-described conditionsare shown in FIGS. 10A to 10C.

[Evaluation]

As shown in FIG. 10C, when setting the storage time of the substrate Wto 120 hours (5 days) (Comparative Example 3), a thick natural oxidefilm is formed on the rear main surface of the substrate W during thestorage. Therefore, even when subjecting the substrate W to the hydrogenheat treatment by separating the substrate W from the susceptor 1, thenatural oxide film cannot be removed sufficiently.

On the other hand, as shown in FIG. 10A, when setting the storage timeof the substrate W to 34 hours (Example 3-1), the natural oxide filmformed on the rear main surface of the substrate W is almost completelyremoved by etching through the hydrogen heat treatment, so that the hazelevel on the whole rear main surface of the silicon epitaxial wafer canbe kept to from 0.1 to 0.5 ppm. Further, as shown in FIG. 10B, whensetting the storage time of the substrate W to 64 hours (2.7 days)(Example 3-2), it becomes difficult to completely remove, through thehydrogen heat treatment, the natural oxide film formed on the rear mainsurface of the substrate W. However, the natural oxide film can beremoved by etching to a degree where the haze level on the whole rearmain surface of the silicon epitaxial wafer is 50 ppm or less. In otherwords, when separating the substrate W from the susceptor 1 to subjectthe substrate W to the hydrogen heat treatment at a temperature of 1000°C. or more within 3 days after the natural oxide film removal cleaning,the haze level on the whole rear main surface of the subsequentlyproduced silicon epitaxial wafer can be suppressed to 50 ppm or less.

Second Embodiment

In a method for producing a silicon epitaxial wafer according to thesecond embodiment, front main surface oxide film formation cleaning(corresponding to ozone water cleaning in a step S103; see FIG. 5) forforming an oxide film on the front main surface of the double-sidedmirror silicon single crystal substrate W is performed as final cleaningof the front main surface of the substrate W in the cleaning stepperformed before the hydrogen heat treatment step.

In other words, in the cleaning step, when performing removal of thenatural oxide film on both the main surfaces, for example, usinghydrofluoric acid as final cleaning of both the main surfaces of thesubstrate W, both the main surfaces of the substrate W treated usinghydrofluoric acid come into a high-activity state. As a result, foreignmatters such as particles are easily adhered to the high-activity frontsurface of the substrate W (see Table 1). When foreign matters such asparticles are once adhered thereto, the removal thereof is not easy.Further, when epitaxially growing the silicon epitaxial layer in a statewhere the foreign matters are adhered to the front main surface, crystaldefects easily occur.

Accordingly, in the method for producing a silicon epitaxial wafer ofthe second embodiment, the cleaning of the front main surface and rearmain surface of the substrate W is performed for each main surfaceusing, for example, a single wafer cleaning device (not shown). In otherwords, the natural oxide film removal cleaning is performed as finalcleaning of the rear main surface of the substrate W in order tosuppress occurrence of the haze. On the other hand, the oxide filmformation cleaning is performed as final cleaning of the front mainsurface in order to suppress adhesion of foreign matters such asparticles.

The method for producing a silicon epitaxial wafer according to thepresent invention will be described below with reference to FIG. 5.

Specifically, as shown in FIG. 5, first, the substrate W is fed, forexample, into the single wafer cleaning device using a predeterminedcarrier. Then, chemicals for SC1 cleaning are sprayed on the front mainsurface of the substrate W from a predetermined nozzle to perform theSC1 cleaning of the front main surface of the substrate W (step S101).Further, chemicals for SC1 cleaning are sprayed also on the rear mainsurface of the substrate W from a predetermined nozzle to perform theSC1 cleaning of the rear main surface of the substrate W (step S201). Bythe SCI cleaning, particles adhered to both the main surfaces of thesubstrate W are removed.

Next, purified water is sprayed on the front main surface of thesubstrate W from a predetermined nozzle to perform a pure water rinse(step S102). Further, purified water is sprayed also on the rear mainsurface of the substrate W from a predetermined nozzle to perform a purewater rinse (step S202).

Subsequently, front main surface oxide film formation cleaning isperformed as final cleaning of the front main surface of the substrateW. In the front main surface oxide film formation cleaning, for example,ozone water cleaning is performed (step S103), and as a result, an ozoneoxide film as an oxide film is formed on the front main surface of thesubstrate W. Specifically, ozone water is sprayed on the front mainsurface of the substrate W from a predetermined nozzle of the cleaningdevice, and as a result, a fine ozone oxide film which is suppressed inadhesion of foreign matters such as particles is formed on the frontmain surface of the substrate W.

Further, rear main surface natural oxide film removal cleaning isperformed as final cleaning of the rear main surface of the substrate W.In the rear main surface natural oxide film removal cleaning, forexample, hydrofluoric acid cleaning is performed (step S203), and as aresult, a natural oxide film formed on the rear main surface of thesubstrate W during the SC1 cleaning in step S201 is removed by etchingusing hydrofluoric acid.

Thereafter, purified water is sprayed on the front main surface of thesubstrate W from a predetermined nozzle to perform a pure water rinse(step S104). Further, purified water is sprayed also on the rear mainsurface of the substrate W from a predetermined nozzle to perform a purewater rinse (step S204).

Next, drying of the substrate W is performed. In the drying of thesubstrate W, for example, spin drying is performed by rotating thesubstrate W at a predetermined speed to remove waterdrops on the frontsurface of the substrate W by a centrifugal force (step S105).

Thus, the cleaning step of the substrate W is completed.

Thereafter, the cleaned substrate W is fed into the vapor phase epitaxyapparatus 100 (step S106) to perform the hydrogen heat treatment step inthe same manner as in the first embodiment. In other words, in thehydrogen heat treatment step, the substrate W is separated from thesusceptor 1 (step S107). In this state, the reactor 2 inside is heated(elevated in temperature) to the hydrogen heat treatment temperaturewhich is considered to be a temperature lower than the vapor phaseepitaxy temperature of the silicon epitaxial layer (step S108) toperform the hydrogen heat treatment (step S109). As a result, an ozoneoxide film on the front main surface of the substrate W exposed to ahydrogen atmosphere within the reactor 2 and a natural oxide film formedon the rear main surface of the substrate W after the cleaning step areremoved by etching using hydrogen. Accordingly, the natural oxide filmon the rear main surface of the substrate W can be evenly removedsurely.

Thereafter, the substrate W is mounted within the spot facing 10 of thesusceptor 1 (step S110). In this state, the substrate W is furthersubjected to the hydrogen heat treatment for a predetermined time, andas a result, the ozone oxide film on the front main surface of thesubstrate W is completely removed. Thus, the hydrogen heat treatment iscompleted.

Next, in the same manner as in the first embodiment, the siliconepitaxial layer is epitaxially grown on the front main surface of thesubstrate W to produce the silicon epitaxial wafer. Then, the producedsilicon epitaxial wafer is taken out from the reactor 2 inside (stepsS111 to 113).

As described above, according to the second embodiment, the front mainsurface oxide film formation cleaning is performed as final cleaning ofthe front main surface of the substrate W in the cleaning step, so thatthe oxide film can be formed on the front main surface of the substrateW. Accordingly, unlike a case where also the front main surface of thesubstrate W is cleaned using hydrofluoric acid as final cleaning in thecleaning step, the front main surface of the substrate W is low in theactivity and therefore, foreign matters such as particles are hardlyadhered, so that occurrence of the crystal defects of the siliconepitaxial layer due to adhesion of the foreign matters can besuppressed.

Incidentally, in the first and second embodiments, during the periodfrom feeding the substrate W into the reactor 2 until completing a stateof separating the substrate W from the susceptor 1, the substrate Wremains in a state of being separated from the susceptor 1. However, thepresent invention is not limited thereto and the substrate W may beseparated from the susceptor 1 only for a predetermined time at leastduring the hydrogen heat treatment step.

Further, separation of the substrate W from the susceptor 1 is performedusing the lift pins 4. However, the present invention is not limitedthereto, and it is needless to say that the substrate W may be separatedfrom the susceptor 1 using any method. Further, separation of thesubstrate W from the susceptor 1 is performed by lowering the susceptor1 relatively to the lift pins 4. However, the present invention is notlimited thereto. For example, using a construction such that the liftpins 4 can be raised with respect to the susceptor 1 irrespective ofvertical movement of the susceptor 1, the substrate W may be separatedfrom the susceptor 1 by raising the lift pins 4.

Further, it can be appropriately changed whether the front main surfacenatural oxide film removal cleaning and rear main surface natural oxidefilm removal cleaning for removing a natural oxide film are performed asfinal cleaning of the front main surface and rear main surface of thesubstrate W in the cleaning step. In the present invention, at least,the substrate W may be separated from the susceptor 1 during thehydrogen heat treatment step and the substrate W may be mounted on thespot facing 10 of the susceptor 1 during the vapor phase epitaxy step.

Example 4 and Comparative Example 4 according to the present inventionwill be described below.

EXAMPLE 4

<Comparison Between Cleaning Conditions>

(Cleaning Conditions)

Example 4: Ozone water cleaning is performed as final cleaning of thefront main surface of the substrate W and hydrofluoric acid cleaning isperformed as final cleaning of the rear main surface of the substrate W.

Comparative Example 4: Hydrofluoric acid cleaning is performed as finalcleaning of both the main surfaces of the substrate W.

(Measurement of the Number of Particles Immediately After the CleaningStep)

Using a light scattering optical surface inspection apparatus, thenumber of particles having a size of 0.12 μm or more in diameter on thefront main surface of the substrate W immediately after the cleaningstep is measured.

(Measurement of the Number of Particles Immediately After the VaporPhase Epitaxy Step)

Using a light scattering optical surface inspection apparatus, thenumber of particles having a size of 0.12 μm or more in diameter on thesilicon epitaxial layer of the silicon epitaxial wafer is measured.

Measurement results of the number of particles in Example 4 andComparative Example 4 are shown in Table 1.

TABLE 1 Example 4 Comparative Example 4 Final Cleaning Front mainsurface: O₃ Front main surface: Rear main surface: HF HF Rear mainsurface: HF Immediately After  0 1.5 × 10³ Cleaning Step (number ofparticles/Substrate) Immediately After 10 25 Vapor Phase Epitaxy Step(number of particles/Wafer)

[Evaluation]

In the case of performing the hydrofluoric acid cleaning as finalcleaning of both the main surfaces of the substrate W (ComparativeExample 4), 1.5×10³ particles per substrate are measured immediatelyafter the cleaning step, and further, 25 particles per silicon epitaxialwafer are measured immediately after the vapor phase epitaxy step.

On the other hand, in the case of performing the ozone water cleaning asfinal cleaning of the front main surface of the substrate W andperforming the hydrofluoric acid cleaning as final cleaning of the rearmain surface of the substrate W (Example 4), no particle having a sizeof 0.12 μm or more in diameter is measured, and further, also the numberof particles to be measured per silicon epitaxial wafer immediatelyafter the vapor phase epitaxy step can be reduced to 10.

Third Embodiment

In a method for producing a silicon epitaxial wafer according to thethird embodiment, there is used a construction such that in the cleaningstep, the front main surface oxide film formation cleaning is performedas final cleaning of the front main surface of the substrate W, forexample, using ozone water as well as the rear main surface naturaloxide film removal cleaning is performed as final cleaning of the rearmain surface of the substrate W, for example, using hydrofluoric acid,the substrate W is then quickly fed into the reactor 2 with anon-oxidation atmosphere and the hydrogen heat treatment step isperformed not in a state of separating the substrate W from thesusceptor 1 but in a state of mounting the substrate W on the spotfacing 10, unlike the first and second embodiments.

When setting to 6 hours or less a time for storing the substrate W inthe air as an oxidizing atmosphere during the period that the substrateW is fed into the reactor 2 with a non-oxidizing atmosphere (e.g., ahydrogen atmosphere) after the final cleaning, a natural oxide filmhaving a thickness at a level causing haze on the rear main surface ofthe silicon epitaxial wafer is hardly formed on the rear main surface ofthe substrate W.

In other words, when setting the storage time in the air to 6 hours orless, the natural oxide film on the rear main surface of the substrate Wis sufficiently removed by etching even when mounting the substrate W onthe spot facing 10 of the susceptor 1 within the reactor 2 andsubjecting the substrate W to the hydrogen heat treatment in thehydrogen heat treatment step. Therefore, in the subsequent vapor phaseepitaxy step, fine unevenness can be prevented from occurring on therear main surface of the substrate W, particularly, on the portions ofthe rear main surface facing the lift pin 4 through-holes 10 a, so thatwhen measuring the haze level using the optical surface inspectionapparatus, the haze level on the whole rear main surface of the siliconepitaxial wafer can be suppressed to 50 ppm or less.

Incidentally, in the second and third embodiments, there is used aconstruction such that in the front main surface oxide film formationcleaning, the ozone oxide film is formed as an oxide film on the frontmain surface of the substrate W. However, the present invention is notlimited thereto and there may be used a construction such that an oxidefilm other than the ozone oxide film is formed.

Further, the present invention is not limited to the above-describedembodiments. For example, the hydrofluoric acid cleaning is performed asthe rear main surface natural oxide film removal cleaning; however,other cleaning methods may be used as long as the natural oxide film onthe rear main surface can be removed.

Further, in the second embodiment, there may be of course used aconstruction that fine particles adhered to the substrate W are removedusing scrub cleaning in place of the SC1 cleaning.

Further, description is made on the susceptor 1 in which the spot facing10 having the upper spot facing section 11 and the lower spot facingsection 12 is formed. However, the shape of the spot facing 10 is notlimited thereto. The shape of the spot facing 10 may be any as long asit is a shape capable of mounting the substrate W.

In addition, the single wafer vapor phase epitaxy apparatus 100 isillustrated as an apparatus for producing the silicon epitaxial wafer.However, the present invention is not limited thereto and a batch vaporphase epitaxy apparatus may be used.

Example 5 and Comparative Example 5 of the present invention will bedescribed below.

EXAMPLE 5

<Relation Between Storage Time in the Air and Haze Level>

(Cleaning Conditions)

Ozone water cleaning is performed as final cleaning of the front mainsurface of the substrate W and hydrofluoric acid cleaning is performedas final cleaning of the rear main surface of the substrate W.

(Storage Time in the Air After Hydrofluoric Acid Cleaning)

Each substrate W after the hydrofluoric acid cleaning is stored in theair for the storage time of 0 hour (herein, when feeding the substrate Winto the reactor 2 within 20 minutes after the hydrofluoric acidcleaning, the storage time is set to 0 hour. FIG. 11A: Example 5-1), 1.5hours (FIG. 11B: Example 5-2), 3 hours (FIG. 11C: Example 5-3), 6 hours(FIG. 11D: Example 5-4), 12 hours (FIG. 12A: Comparative Example 5-1),24 hours (FIG. 12B: Comparative Example 5-2), 48 hours (FIG. 12C:Comparative Example 5-3) and 96 hours (FIG. 12D: Comparative Example5-4). After the completion of the storage time in the air, eachsubstrate W is immediately fed into the reactor 2 with a hydrogenatmosphere, for example, through a load lock chamber with a nitrogenatmosphere.

(Hydrogen Heat Treatment Conditions)

The hydrogen heat treatment temperature is set to 1050° C., and in astate of mounting the substrate W on the susceptor 1, each hydrogen heattreatment is performed while keeping the state for 60 seconds.

Measurement results of the haze level x on the rear main surface of thesilicon epitaxial wafer produced under the above-described conditionsare shown in FIGS. 11A to 11D and FIGS. 12A to 12D.

[Evaluation]

As shown in FIGS. 12A to 12D, when setting the storage time in the airafter cleaning the rear main surface of the substrate W withhydrofluoric acid to 12 hours or more (Comparative Example 5;Comparative Examples 5-1 to 5-4), a natural oxide film is formed on therear main surface of the substrate W during the storage, and as aresult, haze at a level larger than 50 ppm is visualized on the rearmain surface of the silicon epitaxial wafer.

On the contrary, as shown in FIGS. 11A to 11D (Example 5; Examples 5-1to 5-4), as the storage time in the air becomes longer from 0 hour, thehaze level x on the whole rear main surface of the silicon epitaxialwafer more deteriorates; however, when the time for storing thesubstrate W in the air after the hydrofluoric acid cleaning is 6 hoursor less, the haze level x on the whole rear main surface of the siliconepitaxial wafer can be kept to 50 ppm or less even when the substrate Wis not separated from the susceptor 1 during the hydrogen heattreatment.

INDUSTRIAL APPLICABILITY

As described above, the method for producing a silicon epitaxial waferand the silicon epitaxial wafer according to the present invention arecapable of preventing fine unevenness from occurring on the rear mainsurface of the double-sided mirror silicon epitaxial wafer as well asare useful for improving the haze level on the rear main surface of thesilicon epitaxial wafer. Particularly, the producing method of a siliconepitaxial wafer and the silicon epitaxial wafer are capable ofpreventing fine unevenness from occurring on the portions of the rearmain surface of the silicon epitaxial wafer facing the lift pinthrough-holes, as well as are useful when suppressing the haze level onthe whole rear main surface of the silicon epitaxial wafer to 50 ppm orless.

Explanation of Reference Numerals  1 Susceptor  2 Reactor  4 Lift pin 10Spot facing 10a  Through-hole W Doublesided mirror silicon singlecrystal substrate

1. A method for producing a silicon epitaxial wafer, comprising: ahydrogen heat treatment step of arranging a susceptor capable ofmounting a silicon single crystal substrate within a reactor andsubjecting the silicon single crystal substrate mounted on a spot faceof the susceptor to heat treatment in a hydrogen atmosphere; and a vaporphase epitaxy step of epitaxially growing a silicon epitaxial layerafter the hydrogen heat treatment step, wherein the silicon singlecrystal substrate is separated from the susceptor during the hydrogenheat treatment step by allowing a lift pin which vertically moves thesilicon single crystal substrate relatively to the susceptor to supportthe silicon single crystal substrate, and the silicon single crystalsubstrate is mounted on the spot face of the susceptor during the vaporphase epitaxy step, and the hydrogen heat treatment step is performed ata temperature lower than a vapor phase epitaxy temperature of thesilicon epitaxial layer step.
 2. The method for producing the siliconepitaxial wafer as claimed in claim 1, wherein in the hydrogen heattreatment step, a temperature within the reactor when the silicon singlecrystal substrate is separated from the susceptor is at least 900° C. 3.The method for producing the silicon epitaxial wafer as claimed in claim1, further comprising a cleaning step of cleaning the silicon singlecrystal substrate before the hydrogen heat treatment step, wherein thecleaning step has natural oxide film removal cleaning for removing anatural oxide film formed at least on a rear main surface of the siliconsingle crystal substrate, and the natural oxide film removal cleaning isperformed as final cleaning of the rear main surface.
 4. The method forproducing the silicon epitaxial wafer as claimed in claim 3, wherein inthe natural oxide film removal cleaning, the natural oxide film iscleaned and removed using hydrofluoric acid.
 5. The method for producingthe silicon epitaxial wafer as claimed in claim 4, wherein the cleaningstep has front main surface oxide film formation cleaning for forming anoxide film on a front main surface of the silicon single crystalsubstrate, and the front main surface oxide film formation cleaning isperformed as final cleaning of the front main surface.
 6. The method forproducing the silicon epitaxial wafer as claimed in claim 5, wherein atime for the silicon single crystal substrate to be stored in air duringthe period that the substrate is fed into the reactor after the finalcleaning is set within 3 days.
 7. The method for producing the siliconepitaxial wafer as claimed in claim 3, wherein the cleaning step hasfront main surface oxide film formation cleaning for forming an oxidefilm on a front main surface of the silicon single crystal substrate,and the front main surface oxide film formation cleaning is performed asfinal cleaning of the front main surface.
 8. The method for producingthe silicon epitaxial wafer as claimed in claim 7, wherein a time forthe silicon single crystal substrate to be stored in air during theperiod that the substrate is fed into the reactor after the finalcleaning is set within 3 days.
 9. The method for producing the siliconepitaxial wafer as claimed in claim 1, wherein the silicon singlecrystal wafer is a double-sided mirror silicon single crystal substrateof which both the main surfaces are subjected to a mirror polishingfinish.